This invention relates to positive feed power drills having a spindle drive gear train and a spindle feed gear train arranged to be driven by the same motor, and having means for disengaging and locking the spindle feed gear train for reversal of the positive feed drive, and more particularly to a system for holding the feed gear train disengaged from the drive gear train, but unlocked, after the spindle has been retracted and the retracting hydraulic pressure has been removed from the piston.
Positive feed power drills normally have a single motor for turning a spindle through a drive gear train. The spindle is threaded into a feed gear that turns for advancing the spindle as the drill progresses through a work piece. The feed gear is driven by a gear train from the same motor as the drive gear train, but the gear ratio of the drive gear train is selected to be slightly less than the gear ratio of the feed gear train so the feed gear will turn slightly faster than the drive gear. In that way, the spindle is advanced a predetermined amount for each turn through the work piece.
Once the spindle has been advanced sufficiently, a hydraulic piston is actuated to disengage the spindle feed gear train from the drive gear train and lock it in place. As the motor continues to drive the spindle in the same direction, the spindle threads turn inside the locked feed gear to rapidly retract the spindle. Once the spindle has been fully retracted, the hydraulic pressure on the piston is still on, so the feed gear train now rotates at the same rate as the drive gear train, causing the engaging side teeth of the feed coupling gear to ratchet over the fixed teeth until pressure in the piston cylinder has been manually relieved. It would be desirable to provide means for eliminating the ratcheting by automatically removing the hydraulic pressure and holding the feed gear train out of engagement with the drive gear train after the hydraulic pressure is automatically removed from the piston, until such time as the holding means is manually reset to recycle the positive feed drill for another drilling or countersinking cycle.